The present invention relates to cubic boron nitride composite particles, comprising microparticles, preferably hard microparticles, dispersed in cubic boron nitride particles.
Cubic boron nitride is second only to diamond in hardness and has excellent chemical stability greater than that of diamond. Thus, there is increasing demand for cubic boron nitride materials for use in grinding, polishing and cutting. A variety of methods for producing cubic boron nitride have been developed, and the method which is best known and most often employed in industry includes maintaining hexagonal boron nitride under high-temperature, high-pressure conditions (approximately 5.5 GPa and 1600xc2x0 C.) in the presence of a solvent (catalyst), to thereby transform hexagonal boron nitride to cubic boron nitride. Examples of well-known solvents (catalysts) include alkali metal nitrides, alkali metal boronitrides, alkaline earth metal nitrides and alkaline earth metal boronitrides. Particularly, Li3N and Li3BN2 have been confirmed to be effective catalysts (see, e.g., U.S. Pat. No. 3,772,428). Cubic boron nitride produced using such a solvent (catalyst) generally assumes the form of monocrystalline particles which do not contain hetero-microparticles, such as microparticles of heterospecies and cubic boron nitride microparticles having different crystallographic direction.
However, when the aforementioned monocrystalline cubic boron nitride particles are used in grinding or polishing, the particles may be subject to large-scale crushing to thereby lower the grinding ratio. Thus, formation of minute cutting edges may be insufficient, so as to disadvantageously increase the frequency of dressing.
It is therefore an object of the present invention to provide cubic boron nitride materials having enhanced grinding, polishing and cutting properties. The above objective has been achieved by providing:
(1) Cubic boron nitride composite particles comprising microparticles dispersed in cubic boron nitride particles;
(2) Cubic boron nitride composite particles according to (1), wherein the microparticles are dispersed in the cubic boron nitride particles in an amount of from about 1% to about 50% by volume;
(3) Cubic boron nitride composite particles according to (1) or (2), wherein the microparticles have an average particle size of about 10 nm to about 10 xcexcm and a particle size equal to or smaller than one-third the particle size of the cubic boron nitride particles;
(4) Cubic boron nitride composite particles according to (1) or (2), wherein the microparticles comprise hard microparticles; and
(5) Cubic boron nitride composite particles according to (3), wherein the microparticles comprise hard microparticles.
The reason why the cubic boron nitride composite particles of the present invention exhibit excellent performance has not been fully elucidated. However, possible reasons as to why the particles are not subject to large-scale crushing are as follows. Specifically, propagation of cracking is prevented or the direction of cracking propagation is changed by the microparticles, to thereby modify the energy for breaking; and residual stress is generated around microparticles, to thereby absorb energy for breaking. It is considered that the generation of minute cutting edges is promoted because microparticles exposed on the particle surface serve as break-initiating points, to thereby generate microcracks corresponding to the distance between microparticles.
As used herein, the term xe2x80x9cparticlesxe2x80x9d means xe2x80x9cgrainsxe2x80x9d or xe2x80x9ccrystalline particlesxe2x80x9d.